Water (cooling water) is used as a medium (cooling medium) to cool cylinders and cylinder heads in water-cooled engines, including automobile engines, and a fluid pump is provided as a device to forcibly circulate the cooling water in a water jacket formed in the cylinder block of the engine. This type of fluid pump is commonly referred to as a water pump, and includes a pump base formed from a part of the cylinder block in which a cooling water outlet and inlet are formed, a pump body that is installed on the pump base to form a pump chamber, a pump pulley rotatably supported via a bearing (radial bearing) on the outer periphery of the pump body, a pump shaft connected at one end to the pump pulley and that extends into the pump chamber through an aperture in the pump body, and an impeller (vane wheel) installed on the other end of the pump shaft and positioned within the pump chamber. A drive belt connected to the crankshaft of the engine is fitted around the pump pulley, and when the pump pulley rotates when driven by the crankshaft, the pump shaft that is integral with the pump pulley and the impeller also rotate. When the impeller rotates, cooling water is drawn in from the inlet, forced out to the periphery by centrifugal force, and is expelled from the outlet into the water jacket (for example, see Japanese Patent Application Laid-open No. H5-312186, Japanese Patent Application Laid-open No. 2002-349481, and Japanese Patent Application Laid-open No. 2004-84610).
In this type of water pump it is necessary to maintain the leak tightness of the pump chamber, and sealing means is provided in the aperture of the pump body between the pump shaft and the pump body. Sealing means that include a member installed on the pump body (body side seal member) and a member installed on the pump shaft (shaft side seal member) known as a mechanical seal is frequently used as the seal means, and when the two seal members contact a sealing surface is formed.